Method of and apparatus for air temperature regulation



Jan. 14, 1964 c. B. BAVER ETAL 3,117,538

METHOD OF AND APPARATUS FOR AIR TEMPERATURE REGULATION Filed Sept. 30.1960 I 4 Sheets-Sheet 1 TLLE'JT INVENTORS CL V05 8. 34 M52 Y 4 27%? 02EFENDBEEG AT TORNEY Jan. 14, 1964 c. B. BAVER ETAL 3,117,538

METHOD OF AND APPARATUS FOR AIR TEMPERATURE REGULATION Filed Sept. 50,1960 4 Sheets-Sheet 2 a] R Q H INVENTOR-S' CZ YOEB .84 v52 6% marM/kewaama ATTORNEY Jan. 14, 1964 c. B. BAVER ETAL 3,117,538

METHOD OF AND APPARATUS FOR AIR TEMPERATURE REGULATION Filed Sept. 30,1960 4 Sheets-Sheet 3 I i 1 1 72 1 t 5H5 OUT All? IN JNVENTORS 42 yps 3.BA v52 BY Her /012 #Z/kavnazm;

ATTORNEY Jan. 14, 1964 c. B. BAVER ETAL 3,117,533

METHOD OF AND APPARATUS FOR AIR TEMPERATURE REGULATION United StatesPatent 0 3,117,538 METHGD 0F AND APPARATUS FOR AIR TEMEERATUFEREGULATION Clyde B. Beyer and Arthur M. Frendberg, Akron, Qhio,assignors to The Babcoclt 8: Wilcox Company, New York, N.Y., acorporation of New .lersey Filed cpt. 30, 1960, Ser. No. 60,267 5Claims. ((31. 1lt 56) The present invention relates to a fuel firingsystem for a vapor generator, and more particularly to a method of andapparatus for heating and controlling the temperaustre and the rate offlow of both primary and secondary air to a furnace.

in the suspension burning or" solid fuels, for example, pulverizedbituminous coal, the fuel is prepared as required a pulverizer with thefinished product transported directly to a furnace in a carrier streamof air which at the same time also provides the primary air forcombustion. One or" the common applications of pulverized coalcombustion is to produce hot gases for use in generating, superheatingand reheating vapor such as steam. in such services, the combustionefiiciency of the fuel and the etliciency of heat transfer is highlyimportant in providing for the lowest possible operating cost. In thepreparation of the pulverized fuel, such as bituminous coal, the airdelivered to the pulverizing Zone of the pulverizers is advantageouslypreheated to effect moisture removal from the fuel during thepulverization process. For eiliciency, bo h as to combustion and as toheat transfer in the unit, it is desirable to preheat the primarycombustion air, or carrier air, to a value necessary to effect the dr'ing of the fuel with a minimum addition of tempering or atmospheretemperature As pert of the efficient combustion process, it is desirableto preheat secondary combustion air o as to reclaim heat from the cooledgases leaving the heat exchange surfaces of the vapor generating unit.Frequently, the temperature and pressure requirements or" the primaryand sec .lary air are difierent and in effecting the optimum heatrecovery from the gases of combustion it is desirable to maintain thetemperature of the gases discharged to the atmosphere at a preselectedvalue. It is, of course, desirable, and well known in the art, to avoidcooling the spent heating gases to a value below their dew pointtemperature so as to avoid corrosion in the metallic parts in contactwith such low temperature heating gases.

he present invention, the gases or" combustion leaving a vaporgenerating, superheating and reheating unit are passed through a plenumchamber having multiple outlets for the movement of the cooled heatinggases through selected flow paths to air heating urits. The primary andsecondary air heaters are entirely separate and are arranged in parallelwith control means provided to properly divide the gas flow to theseparate air heaters for selective heating of the primary and secondarycombustion The control or" gas flow is accomplished by a single valvemeans which selectively regulates the fiOW of the pr per amount of gasover the heating surfaces of the primary air heater so as to maint a asubstantially uniform gas outlet temperature from the air heaterregardless of the flow of pr' nary air through the primary air heater.The remainder of the cooled heating gases is passed through thesecondary air heaters with the temperature of the gases leaving theseheaters allowed to vary in accordance with the flow through thesecondary air heaters. However, the variation in gas temperature leavingthe secondary air heaters is relatively minor and is substantially equalto the controlled temperature of the gases leaving the primary airheater.

- 0 I H The various features of novelty which characterize our inventionau'e pointed out with particularity in the claims annexed to and forminga part of this specification. For a better understanding of theinvention, its operating advantages and specific objects attained by itsuse, reference should be had to the accompanying drawiu s anddescriptive matter in which we have illustrated and described apreferred embodiment of the invention.

Of the drawings:

PEG. 1 is an elevation, partly in section, of a pulverized fuel firingsystem constructed and arranged according to the present invention asapplied in the generation and heating of vapor;

FIG. 2 is a plan, partly in section, of a portion of the apparatus shownin PEG. 1 and taken on the line 22;

FIG. 3 is an elevation, partly in section, or" a portion of theapparatus shown in FIG. 2 and taken on the line 3I'-;; and

FIG. 4 is a schematic showing of the air flow circuit of the apparatusshown in FEGS. 1 to 3, inclusive.

In the embodiment of the invention illustrated in the drawings, a highcapacity vapor generating, superheating and reheating unit of knownconstruction is supplied with pulverized coal from a plurality of d ectfiring pulverizer The gases of combustion produced in burning the coalare passed upwardly through the unit giving up some portion of theirheat content by radiation of the surroun ing iluid cooled walls of thefurnace. Thereafter, the gases of combustion are mover la a downwarddirection over and between convection heat exchange elements fordischarge to the air heaters of the present invention.

As shown particularly in 1 an upwardly elongated furnace it? havingfluid cooled wall tubes 11 therein is supplied with pulverized coalthrough a plurality of burners 12 positioned in oppos' e walls of thefurnace. The burners are supplied with a; -borne pulverized coal from aplurality of direct fired air swept pulverizers 13. Secondary combustionair is supplied to the furnace, through the burners, from a'windb-ox 7i?enclosing all of the burners. Preheated secondary air is deli ered tothe windbox '76? on each side or" the furnace it by a duct 71. In. theexample shown in the drawings, ten pulverizcrs are used to provide thepulverized coal for the furnace. As hereinafter described, each of thepulverizers is provided with primary air from a commo'rduct or manifoldM which transports high pressure, 1 gh temperature air to thepulverizers. A single p any air fan 15, with a duplicate fan for standbyservice, provides the which is assed through a duct 23 to a tubular airheater 1e, delivering heated air to the manifold M for selectivelysupplying each of the pulverizers 13 With hot primary air. A branch ductor manifold 1'7 opens to the discharge side of the fan 15 upstream ofthe primary air heater 16, with the relatively cold from this sourcebeing also selectiv ly controlled for delivery of tempering to each ofthe pulverizers when desired.

As shown in FIGS. 2 and 3, the vapor generating unit is provided with aplurality of rotary regenerative air heaters 33. These heaters 15 arepositioned in groups of two on opposite sides of the centerline of theunit and the tubular recuperative primary air heater 16. As shownparticularly in FIG. 3, each of the secondary air heaters is providedwith an economizer tube section 2%"? upstream of the air heater anddownstream of the plenum chamber 21 for the gases discharged from theconvection bank of the vapor generating unit.

The plenum chamber 2?. (see FIGS. 1 and 3) receives partially cooledgases from the convection bank of the vapor generator where the gasesflow in p rallel through separate heat exchange paths 22 and 23 dividedby an upright tube bafi'le 24 and containing superheating and reheatingsurfaces (not shown). Each of the parallel gas passes is provided withdampers and 26 respectively at the discharge end of the convection gaspasses so that the distribution of heating gases through the convectionbank may be controlled for regulation of superheat and reheattemperatures. The plenum chamber 21 is provided with a single, centrallylocated lower outlet 27' which leads to the tubular type of primary airheater 1:). In addition, the plenum chamber is provided with gas outlets28 on the rearward side of the unit which open into walls 3% defininggas flow passes directing the gas flow downwardly over the economizersurfaces 28 and into the secondary air heaters 18.

As shown in FIGS. 1 and 3, the hot gases leaving the plenum chamber 21and moving downwardly over the ecouomizer surraces 26 enter the rotaryregenerative air heaters 18 to pass therethrough and discharge throughthe gas outlet 33 for movement to a stack (not shown). The incoming airenters each of the secondary air heaters 15 through a duct 72 and isdischarged through a duct 73 into a common collecting duct 74- for flowthrough duct 71 to the wind boxes 70.

As shown in FIG. 1, the primary air heater 16 is provided with rows ofupright tubes 31 extending between upper and lower tube sheets 32 and33, respectively. As shown, one half of the tubes 31 form a downflowpath for the heating gases opening into a gas receiving and turningchamber 3- positioned below the lower tube sheet 33. The chamber 34 ofthe heater is divided by a partition 35 having damper means 36 of thelouvre type positioned in an opening 35' in the partition. Thecombustion gases discharging from the downflow portion of the tubularair heater pass through the dampered opening 35' in the partition 35 andmove upwardly through the remaining upflow portion of the tubes 31todischarge through a gas outlet 37 at the top of the air heater to astack (not shown).

A schematic drawing of the primary and secondary air flow system, withparticular emphasis on the primary air flow path, is shown in FIG. 4. Itwill be noted that each of the regenerative secondary air heaters 18 isprovided with an individual forced draft fan 46. It is intended that atrated capacity of the unit all four fans will be in operationdischarging air into the secondary air preheat-ers 1S and thence throughducts 73 into a common secondary air duct '74.

Each of the fans id is provided with a bypass duct bypassing thesecondary air preheater 18. The bypass duct, as well as the secondaryair duct '73 on the downstream side of each of the secondary air heaters18 is provided with manually operated shut-off valves 44 and 45respectively. An additional air discharge duct 46 is connected to thedischarge side of each forced draft fan 4% before the secondary airpreheater with the duct opening to the common cold primary air duct 41.This additional duct 46 is also provided with a manually operatedshut-off damper a With the damper arrangement described, it is possibleto discontinue operation of one or more of the force draft fans 4% andassociated secondary air heater 18, utilizing the remaining forced draftfans to provide both the primary and secondary combustion air for thevapor generating unit.

The primary duct i-1 receives air from the forced draft fans at atemperature of 106 to 150 F. due to the Work of compression of the airin the fans The duct 41 is provided with connections 43 to the inletside of the duplicate primary air fans 15. Either one of the primary airfans has a capacity sufficient to supply primary airto all of the tenpulverizers serving the vapor generating unit. The inlet connection 43leading to each of the primary air fans is provided with a controldamper 5% while each of the outlet ducts 51 from each of the fans isprovided with a manually controlled shut-off damper 52; adjacent the fanoutlets and before the outlet ducts are combined for discharge into thetubular primary air heater 16.

The air passed through the primary air heater i6 is discharged into acommon hot primary air manifold 14 which in turn is provided with a ductconnection 53 to each of the pulverizers. The primary air system is alsoprovided with a bypass duct 54 opening to the outlet side of the primaryair fan 15 ahead of the air heater 16 and discharging tempering air tothe manifold 17 which is likewise provided with individual offtake pipesor ducts 55 leading to each of the pulverizers 13.

With the arrangement described, the flow of air through the primary airfan 15, the tubular air heater 16 and the primary air manifolds 14 and17 is regulated in accordance with the requirements of the temperatureand quantity of air necessary to operate the pulverizers in use. In thisconnection, it will be noted in both the schematic showing of FIG. 4 andin FIG. 1 that control dampers 5:5 and 57 are provided in the ducts 53and 55 leading to each pulverizer while a total primary air fiow controldamper 53 is located adjacent the pulverizer inlet.

in the operation of the pulverizers, the positioning of the total airflow control damper S8 is regulated in accordance with the fuelrequirements from each pulverizer. The pulverizer control system used inthe illustrated embodiment of the invention is similar to that disclosedin U.S. Patent 1,965,643 where the rate of coal flow to the pulverizeris reguated in predetermined ratio to the rate of primary air flow tothe pulverizer.

A separate temperature control is provided for each of the pulverizerswhere the temperature of the coal and air mixture leaving eachpulverizer is measured and recorded. This controller 69 (see FIG. 1) maybe adjusted for any desired coal and air mixture temperature leaving thepulverizer as, for example, F. The temperature controller 6% thusregulates the positioning of the dampers S6 and 57 in the hot air duct53 and the tempering air duct 55 leading to each pulverizer. Forexample, if the temperature of the coal and air mixture leaving apulverizer falls below the preset value of the controller 69, thecontrol will move the damper 57 in a closing direction and movesimultaneously, in an opening direction, the hot air damper 56. The endeffect of this damper regulation will be to increase the temperature ofthe air entering the pul verizer and with stabilized conditions withinthe pulverizer, the temperature of the coal and air mixture leaving willalso be raised to the selected preset value.

The temperature regulation, as described in the preceding paragraph is,of course, dependent upon the availability of sufiicient hightemperature air in the hot air manifold. Any increase in flow throughthe hot air manifold will tend to decrease the temperature of theheating gases leaving the outlet 37 from the tubular air heater 16.Under these conditions, it will be necessary to increase the flow ofheating gases through the air heater 16 to avoid corrosion difficultiesand to compensate for the need for additional high temperature air. Thisis accomplished by the control arrangement shown in FIG. 1. It is, ofcourse, understood that higher air temperature can be obtained at theexpense in overall unit efiiciency by operating at a higher primary airheater gas outlet temperature.

As shown in FIG. 1, the temperature of the air entering the primary airheater 16 is measured by a thermostatic transmitter 61 and the impulsetransmitted to an averaging relay 62 where the impulse is joined by animpulse representative of the temperature of the gases leaving theprimary air heater as measured by a thermostatic transmitter 63. Theaveraged impulse transmitted by the averaging relay 62 is passed througha standardizing relay and a manual selector switch and is effective inactuating an air heater damper control drive 64 which in turn adjuststhe position of the damper 36 shown in FIG. 1. Repositioning the damper36 in accordance with the average of the gas outlet and air inlettemperatures will increase or decrease the flow of gases through theprimary air heater 16 and thereby increase or decrease the temperatureof the air delivered by the heater.

It will be recognized that under stabilized operating conditions, anincrease in the gas flow through the pri- 5 mary air heater 16 willdecreasethe corresponding flow of gas through the secondary air heaters16. However, the effect of decrease or increase in gas flow through thesecondary air heaters is relatively inconsequential with respect to thetemperature of the air leaving the secondary air heaters. This is due tothe comparatively small percentage of the total gas which passes throughthe primary air heater. Ordinarily, the primary air heater 16 willreceive between 15 and 20% of the total gas flow discharging from thevapor generating unit, and a slight change in the primary air heater gasflow will, from a percentage viewpoint, result in only a minorfractional change in the total gas flow through the secondary airheaters 13, with slight change in the exiting air or as temperatures.

In the embodiment of the invention shown in the drawings, the boilerunit has a rated continuous capacity of 3,850,000 pounds of steam perhour at a superheater outlet }SSUIS of 2-450 p.s.i.a. and a temperatureof '1050" F. The reheater of the unit will heat 2,750,060 pounds ofsteam per hour at a pressure of 485 p.s.i.a. (leaving), with theentering steam temperature at 687 F. and with a leaving temperature of1003 F. Under these conditions, 427,000 pounds of coal per hour will beburned and the flue gas weight leaving the secondary air heaters will be4,615,000 pounds per hour, while 3,587,000 pounds of air will be heatedto a temper ture of 550 F. The weight of a gas passed through theprimary air heater will be 393,060 pounds per hour (for maximumtemperature of 580 F), while the quantity of primary air will be 703,000pounds per hour.

With a primary air temperature of 580 F., the pulerizers cansuccessfully handle coal having a surface moisture content of as much as12% during the pulverization process. Under usual operating conditions,the actual moisture content Jill be less and 5 80 F. air temperaturewill be unnecessary. Thus, the temperature of the air entering the pulveer be lower, with the lower temperature attained by reducing the rate ofgas flow through the primary air heater, so as to obtain lower airtemperatures leaving the air heater. Alternatively, the hot air enteringthe pulverizer may be tempered by admitting tempering air from duct 17so that the mixture will be at a temperature corresponding to theselected coal-air mixture temperature leaving the pulverizer. With theblending of hot and cold air to attain a desired air temperature, therate of air flow through the primary air heater will be reduced so thatthe control will also reduce the rate of hot gas flow therethrough tomaintain the desired gas outlet temperature.

In the prefe d operation of tie apparatus, the term perature of the hotair to the pulverizer will closely approximate the air temperaturerequired to process the fuel during pulverization, and a minimum amountof tempering air will be used. it will be understood that some temperairmay be required however since the moisture content of the 'uel deliveredto individual pulverizers may differ, thus requiring a slight differencein the air temperature delivered to individual pulverizers. Highestoverall unit eficiencies will be attained when a minimum amount of ternering air is used in the primary air delivered to the pulverizers.

While it is recognized that the foregoing relates to stabiiizedoperation of a steam generating unit, it will be observed that thecontrol apparatus here disclosed will function in an analogous manner toprovide the predetermined primary air temperature required for the usualload range of a unit and for customary variations in the characteristicsof the fuel.

While in accordance with the provisions of the statutes we haveillustrated and described herein the best form and mode of operation ofthe invention now known to us, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by our claims, andthat certain features of our invention may sometimes be used toadvantage without a corresponding use of other features.

What is claimed is:

1. In a pulverized fuel system comprising, a furnace, a plurality ofburners in saidfurnace, a plurality of pulverizers supplying saidburners with air-borne fuel, means forming a gas passage to receive thegases produced in said furnace, a secondary air heater disposed in saidpassage in which secondary combustion air is heated by gases produced insaid furnace, .economizer means disposed in said passage upstream ofsaid secondary air heater, means for causing secondary air to flowthrough said air heater to each of the burners at a predeterminedpressure, a separate air heater in which primary air is heated byindirect contact with heating gases from said furnace, said primary airheater disposed in said passage and said secondary air heater witheconomizer means being arranged in parallel relationship relative toheating gas flow in said passage, means including a primary air line forcausing primary air to flow through said primary air heater to thepulverizers and thence to said burners, and means for regulating therate of flow of heating gas through said primary air heater inaccordance with the difference in the temperature of the gases leavingsaid primary air heater and the temperature of the air entering saidprimary air heater while the remainder of said heating gas passesthrough said secondary air heater.

2. In a pulverized fuel system comprising, a furnace, a plurality ofburners in said furnace, a plurality of pulverizers supplying saidburners with air-borne fuel, means forming a gas passage to receive thegases produced in said furnace, a secondary air heater disposed in saidpassage in which secondary combustion air is heated by gases produced insaid furnace, means for causing secondary air to flow through said airheater to each of the burners at a predetermined pressure, a separateair heater disposed in said passage in which primary air is heated byindirect contact with heating gases from said furnace, said primary airheater and said secondary air heater being arranged in parallelrelationship relative to heating gas fiow in said passage, meansincluding a primary air line for causing primary air to flow throughsaid primary air heater to the pulverizers and thence to said burners,and means for regulating the rate of flow of heating gas through saidprimary air heater in accordance with the difference in the temperatureof the gases leaving said primary air heater and the temperatrue of theair entering said primary air heater while the remainder of said heatinggas passes though said secondary air heater.

3. A pulverized fuel system according to claim 2 including means forintroducing cold primary air into each of said pulverizers, and meansfor regulating the rate of how of hot and cold primary air to each ofsaid pulverizers.

4. A pulverized fuel system according to claim 3 wherein the rate offlow of hot and cold primary air to each of said pulverizers isregulated in response to the temperature of the fuel and air mixtureleaving each of said pulverizers.

5. The method of operating a pulverized fuel fired vapor generating andheating unit having a furnace, a plurality of burners in said furnace, aplurality of pulverizers supplying said burners with air-borne fuel, asecondary air eater in which secondary combustion air is heated by gasesproduced in said furnace, means for causing secondary air to flowthrough said air heater to each of the burners at a predeterminedpressure, a separate air heater in which primary air is heated byindirect contact with heating gases from said furnace which comprisesburning pulverized fuel in said unit to produce high temperature heatinggases, cooling said high temperature gases in the generation and heatingof vapor, passing a portion of said cooled heating gases through aprimary air heating zone and thence to the atmosphere, passing theheated primary air from said primary air heating zone through 7 apulverizing zone in a quantity in selected ratio to the fuel beingpulverized in said pulverizing zone, passing the mixture of primary airand pulverized fuel to said vapor generating and heating unit, pass ingthe remaining portion of said cooled heating gases through a secondaryair heating zone and thence to the atmosphere, passing said heatedsecondary air from said secondary air heating zone to said vaporgenerating and heating unit to combine With said pulverized fuel inproducing said high temperature heating gases, and controlling thequantity of cooled heating gases passed through said primary air heatingzone in direct response to changes in the differential temperature ofthe air entering and the gas leaving said primary air heating zone.

References Cited in the file of this patent UNXTED STATES PATENTS1,941,365 Patterson et al. Dec. 26, 1933 2,230,799 Hobb Feb. 4, 194.12,321,129 Cooper June 8, 1943 10 2,655,138 Falla Oct. 13, 1953

1. IN A PULVERIZED FUEL SYSTEM COMPRISING, A FURNACE, A PLURALITY OFBURNERS IN SAID FURNACE, A PLURALITY OF PULVERIZERS SUPPLYING SAIDBURNERS WITH AIR-BORNE FUEL, MEANS FORMING A GAS PASSAGE TO RECEIVE THEGASES PRODUCED IN SAID FURNACE, A SECONDARY AIR HEATER DISPOSED IN SAIDPASSAGE IN WHICH SECONDARY COMBUSTION AIR IS HEATED BY GASES PRODUCED INSAID FURNACE, ECONOMIZER MEANS DISPOSED IN SAID PASSAGE UPSTREAM OF SAIDSECONDARY AIR HEATER, MEANS FOR CAUSING SECONDARY AIR TO FLOW THROUGHSAID AIR HEATER TO EACH OF THE BURNERS AT A PREDETERMINED PRESSURE, ASEPARATE AIR HEATER IN WHICH PRIMARY AIR IS HEATED BY INDIRECT CONTACTWITH HEATING GASES FROM SAID FURNACE, SAID PRIMARY AIR HEATER DISPOSEDIN SAID PASSAGE AND SAID SECONDARY AIR HEATER WITH ECONOMIZER MEANSBEING ARRANGED IN PARALLEL RELATIONSHIP RELATIVE TO HEATING GAS FLOW INSAID PASSAGE, MEANS INCLUDING A PRIMARY AIR LINE FOR CAUSING PRIMARY AIRTO FLOW THROUGH SAID PRIMARY AIR HEATER TO THE PULVERIZERS AND THENCE TOSAID BURNERS, AND MEANS FOR REGULATING THE RATE OF FLOW OF HEATING GASTHROUGH SAID PRIMARY AIR HEATER IN ACCORDANCE WITH THE DIFFERENCE IN THETEMPERATURE OF THE GASES LEAVING SAID PRIMARY AIR HEATER AND THETEMPERATURE OF THE AIR ENTERING SAID PRIMARY AIR HEATER WHILE THEREMAINDER OF SAID HEATING GAS PASSES THROUGH SAID SECONDARY AIR HEATER.